There is no objective truth because humans are inherently ideological beings and what we consider objective is just a reflection of our ideology.
Consider markets - a capitalist's "objective truth" might be that they are the most efficient mechanism of allocating resources, a marxists "objective truth" might be that they are a mechanism for exploiting the working class and making the capitalist class even richer.
Consider markets - a capitalist's "objective truth" might be that they are the most efficient mechanism of allocating resources, a marxists "objective truth" might be that they are a mechanism for exploiting the working class and making the capitalist class even richer.
Here's Zizek, famous ideology expert, describing this mechanism via film analysis: https://www.youtube.com/watch?v=TVwKjGbz60k